Episode 26 - Bonus Episode! The Dreaded Heatstroke and SIRS

1.The GP hook

The dreaded heatstroke case isn’t just about temperature. When a hyperthermic dog tips into SIRS and distributive shock, you’re firefighting multi‑organ dysfunction while keeping owners with you. This is our stepwise GP playbook—what we actually do, what to watch and where the pitfalls lurk.

The dreaded heatstroke case isn’t just about temperature. When a hyperthermic patient tips into SIRS and distributive shock you’re firefighting multi‑organ inflammation while keeping owners with you. This is a practical, stepwise GP playbook — what we actually do, what to watch for and where the pitfalls lurk.

2.Why SIRS and heatstroke are inseparable

• SIRS = systemic inflammatory response to a major insult. That insult can be infectious (sepsis) or sterile (trauma, pancreatitis, burns, heat exposure).
• Heatstroke is hyperthermia that triggers that same SIRS cascade.
• In the sickest patients the downstream SIRS effects — vasodilation, capillary leak, tissue hypoperfusion and multi‑organ dysfunction (MODS) — usually determine outcome. Cooling is essential but, in severe cases, often only a small part of the treatment.

3.Spotting distributive (vasodilatory) shock

Distributive shock can look surprisingly “hyperdynamic” — and that’s the clue:

Quick clinical differentiation

Many patients sit between both. Treat what you see and reassess often.

Tip: that sharp “tap” femoral pulse is very characteristic. If you feel it, think distributive shock and watch for SIRS progression.

• Dogs: brick‑red mucous membranes, very brisk CRT, bounding/tapping femoral pulses, tachycardia with hypotension.
• Cats: signs are often subtler — they can go bradycardic or pallid when very sick.
• Common non‑infectious causes: heatstroke, anaphylaxis, neurogenic shock. Hypovolaemia and distributive shock frequently coexist.
• Vasodilatory shock: injected gums, fast CRT, bounding pulses, hypotension.
• Hypovolaemic shock: pale gums, slow CRT, weak pulses, hypotension.

4.First 10 minutes: triage and reliable defaults

If a patient is collapsed or struggling, do these reliably:

Avoid over‑bolusing distributive shock: once fluid responsiveness stops, more crystalloids won’t fix vasodilation and may worsen pulmonary or renal injury.

• Give oxygen immediately (flow‑by, nasal prongs; intubate early if cyanotic or collapsed).
• Provide analgesia/sedation for distress — pick what your team can safely monitor.
• Place IV access and draw blood at the same time (save a re‑stick).
• Start cautious fluid resuscitation if there’s evidence of fluid responsiveness — give small boluses and reassess rapidly.
• Reassess perfusion, heart rate and blood pressure after each bolus. If there’s no meaningful improvement, stop chasing fluids and pivot.

5.When fluids won’t fix it: vasopressors and a reality check

Practical logistics: when you run a pressor CRI have a nurse 1:1, a clear chart for titration and pre‑defined review points.

• If MAP remains low despite reasonable fluid attempts and the picture fits vasodilatory shock, vasopressors are indicated.
• Noradrenaline (norepinephrine) is the usual first‑line pressor in many UK centres. Start low and titrate; follow local ECC protocol for preparation and administration.
• Peripheral continuous infusions are used in emergencies in practice, but the IV must be rock‑solid and monitored closely; a central line is preferable if you can place one safely.
• If you don’t have drugs, staffing or monitoring to run a pressor CRI safely, set limits and consider timely referral or an early honest conversation with the owner about prognosis and options.
• Adrenaline CRIs are sometimes used as a last‑resort when noradrenaline isn’t available — phone a referral centre for dosing and safety before you improvise.

6.The heart often looks weak — T‑POCUS and inotropy

Put the probe on. Poor contractility → consider inotrope; bilateral B‑lines → think aspiration, pulmonary oedema or evolving ARDS‑type lung injury.

• A quick T‑POCUS (30 seconds) is incredibly helpful: subjective contractility assessment often changes management. A “flatter” heart with tiny movements is obvious even without formal echo skills.
• If contractility is poor, consider inotropic support. In GP practice, injectable pimobendan is commonly discussed as an option — check product licence, local policy and get informed owner consent (use may be off‑label).
• If vasopressors plus inotropy aren’t enough, consider critical illness‑related corticosteroid insufficiency (CIRCI) as a possible contributor. Physiological corticosteroid replacement is an advanced intervention — phone a referral centre for guidance on indications and preparations.

7.Bloods that actually help in the next hour

Run what’s available in‑house and recheck frequently (hours, not days):

Sampling at the time of the first IV placement saves you when the patient becomes more unstable.

• Haematology: neutrophilia early, then severe neutropaenia later — a late neutropaenia is a poor prognostic sign. Thrombocytopenia is common and may progress to DIC. On smears, nucleated RBCs in heatstroke are associated with worse outcome.
• Biochemistry: albumin often drops because of capillary leak. Track kidney and liver values for evolving dysfunction.
• Electrolytes: potassium can be low early then rise with AKI. Monitor frequently and adapt therapy.
• Glucose: stress hyperglycaemia is common. A persistently falling or low glucose is worrying and should trigger action (bolus/CRI as appropriate).
• Coagulation: if PT/aPTT are available, follow them; if not, watch for petechiae, bruising and bleeding from catheter sites.

8.Ultrasound: small scans, big decisions

• Chest POCUS: pleural effusion you can tap; B‑lines suggest aspiration, pulmonary oedema or evolving ARDS‑type lung injury.
• Abdomen: fluid‑filled or necrotic‑looking gut supports severe AHDS/HGE‑type patterns and raises concern for bacterial translocation/sepsis.
• Aim for focused scans that answer immediate questions rather than a full diagnostic work‑up.

9.Two common “heat” phenotypes and how they differ

A) Brachycephalics (the airway/distress problem)

B) “True” heatstroke (hours trapped, prolonged hyperthermia, status epilepticus)

• Often present panting, cyanotic, frothing and in respiratory distress.
• Priorities: reduce distress, oxygen, intubate if necessary (cuff the tube and elevate the head), and active cooling.
• Sedation choices depend on team/location: medetomidine (titrated) provides controllable sedation; ACP can be pragmatic in GP settings because it’s long‑acting and lowers core temperature; butorphanol is a very useful adjunct for dyspnoea/distress.
• A short course of anti‑inflammatory corticosteroid is sometimes used if airway inflammation is marked — weigh contraindications and discuss with colleagues.
• Often arrive already well into SIRS and evolving MODS.
• Immediate priorities: oxygen, analgesia/sedation, intubation with a cuffed tube and head elevation, and aggressive active cooling.
• Anticipate complications over hours: haemorrhagic diarrhoea, aspiration/ARDS, refractory hypotension needing vasopressors, hypoglycaemia, coagulopathy, AKI with oliguria/anuria, arrhythmias and generalized oedema/bleeding from line sites.

10.Cooling — how and when to stop

• Actively cool patients with high temperatures: flowing water, fans/air conditioning, clip heavy coats, evaporative techniques. Wet the coat thoroughly and keep evaporative airflow — do not cover the patient with wet towels (they can insulate).
• Surgical spirit (used judiciously on pads/paws in some clinics), fans, ice packs and clipper kit are useful adjuncts.
• Stop active cooling when the patient reaches your local target or shows clinical improvement; aggressive cooling commonly leads to hypothermia, so be ready to dry and warm.

11.Communication, team and logistics in GP

Practical SOPs and a “cooling kit” in prep are surprisingly helpful: clippers, spare fans, surgical spirit, towels, thermometer, nasal prongs, small ET tubes, syringes/ties, and a clear plan for who does what.

• Set boundaries early and be realistic: say openly when the prognosis is uncertain and rapid deterioration is possible.
• Agree review points (e.g. hourly) and predefine triggers for re‑discussion (refractory hypotension despite pressors, anuria despite efforts, escalating coagulopathy).
• Use plain, compassionate language — owners often feel huge guilt. “Severe inflammation” or “sterile sepsis” can help understanding.
• Time‑boxed trials of intensive therapy are acceptable; revisit decisions if predefined goals aren’t met.
• These cases can consume a clinic for many hours. It’s acceptable to set limits if staffing or kit make high‑intensity care unsafe.
• Phone a referral centre early for dose/safety checks and a second opinion.

12.Practical clinical tips

Concise takeaway

You won’t save every case — some will break your heart — but calm, clear, kind care and an organised, stepwise approach give the best chance.

• Don’t assume a “normal” temperature means the patient is fine — owners often start cooling en route; the insult and downstream inflammation may already be underway.
• If you can only do a little POCUS, focus on contractility and B‑lines — both are actionable.
• If fluids stop working, stop flooding the patient: consider pressors and inotropes rather than blind bolusing.
• Use butorphanol liberally for distress/dyspnoea — it helps breathing and comfort.
• Protect the airway: cuff the ET tube and elevate the head; aspiration and regurgitation are common.
• Heatstroke is a SIRS problem: cooling is essential but often not sufficient once the inflammatory cascade has started.
• Do the basics brilliantly: oxygen, analgesia/sedation, IV access, focused bloods, early POCUS, and targeted fluids with frequent reassessment.
• If hypotension persists despite sensible fluids, escalate to vasopressors (and consider inotropy if contractility is poor); call referral centres when unsure.
• Communicate early and honestly with owners, set review points and clear goals, and protect your team and clinic by recognising when the case exceeds what you can safely provide.